Typical ocular surgery, such as, for example, cataract surgery, is routinely performed without the aid of specialized imaging equipment or procedures beyond an operation microscope. However, in the case of a complex or otherwise difficult ocular surgery, including but not limited to lens refilling following capsulorhexis procedures, a surgeon would benefit greatly from the aid of a real time, cross-sectional view. For example, during cataract or other ocular surgical procedures, such a real time, cross-sectional view of the crystalline lens would greatly enhance the surgeon's ability to complete the procedure.
Optical coherence tomography (OCT) is a noninvasive imaging technique that measures backscattered light as a function of depth to provide subsurface imaging with high spatial resolution in three dimensions with no contact needed between the probe and the tissue. An OCT system uses an interferometer in which light from a broadband source is split between illuminating the sample of interest and a reference path. The interference pattern of light reflected or backscattered from the sample and light from the reference delay is used to produce an image of the sample.
Types of OCT include time domain OCT (TD-OCT) and Fourier domain OCT (FD-OCT). In TD-OCT the interference pattern is obtained by scanning the reference path delay and detecting the resulting interferogram pattern as a function of the delay. In FD-OCT, sample light is mixed with reference light at a fixed group delay as a function of optical wave number to obtain the interferogram pattern. FD-OCT has been shown to result in images with an improved signal to noise ratio (SNR). Two types of FD-OCT are typically used: spectral domain OCT (SD-OCT) and swept-source OCT (SS-OCT). SDOCT uses a broadband light source and a dispersive spectrometer in the detector arm. SS-OCT time-encodes the wave number by rapidly tuning a narrowband source through a broad optical bandwidth.
While OCT technology would appear to be beneficial in the context of cataract surgery, it has to date been used mostly for diagnostic purposes. One of the limitations of presently known OCT technology that prevents its use for surgery is the limited scan depth that is obtainable.
OCT systems are described in U.S. Patent Publication Number US 2009/0257065, and U.S. Pat. Nos. 5,493,109; 6,004,314; 7,699,468, all of which are incorporated by reference herein, as if made a part of this specification.
Embodiments of an OCT system with a reference arm optical switch are described in U.S. Patent Application Publication US 2011/0102802 A1, also incorporated by reference herein, as if made a part of this specification. This patent publication describes using the switch to image two distinct structures independently.